A simple method of filtering such solutions is to pass them through purified sheep’s wool, or spun glass, a quantity of which is placed in the tube of the funnel. The whole apparatus may be placed in a warm oven during the process, or the drying box may be utilised for the purpose. [F] [Illustration: _Fig. 1._] The above description not perhaps being perfectly clear, and having been unable to obtain any further description, I give a sketch (_Fig. 1._) of an apparatus found to answer well for the filtration of gelatine solutions and other viscid bodies. =A= is a glass flask, =B= a rubber stopper, =C= a funnel containing a filtering medium of washleather, =D= a tube attached to a three-way cock =E=; one hand manipulates the latter, while the other works the piston =F= of a syringe =G=.—TRANS. =Printing Frames= of different sizes will be found to hand in the photographic studio, and may be utilised without alteration for printing the collotype plates, if they are deep and strong enough to bear the necessary pressure, which is usually applied through the medium of springs; these are better removed, and wooden wedges inserted in their stead between the cross-bars and the loose wooden back of the frames, as by these means far more pressure may be applied. By lifting the one half of the hinged back of the printing frame an examination by transmitted light of the collotype plate may be made and an experienced operator will in this manner judge the exposure of the plate. =The Actinometer= is, however, recommended, particularly for a beginner, as it greatly aids in forming a correct idea of the exposure.